The powertrain of a land vehicle commonly has an internal combustion engine that supplies power and torque to one or more drive wheels via a drivetrain. The drivetrain typically has clutch or a torque converter. An internal combustion engine, and in particular a reciprocating engine, has a minimum rotational speed at which it can operate and deliver torque. Rotational speed is understood as the number of rotations or revolutions per unit time. The clutch or the torque converter allows for a slippage between the combustion engine and the drive wheels, so that the combustion engine can operate with the drive wheels being still or rotating slower than the rotation of the combustion engine.
In the drivetrain, the clutch or torque converter is typically followed by a gearbox, which in turn is coupled to a final drive. The gearbox may be manually or automatically operated, and stepwise or continuously variable. The final drive typically has a fixed gear ratio that is greater than one, thus delivering an output torque that is greater than its input torque. The final drive has the function converting the output torque from the gear switching mechanism of the gearbox to an output torque that is suitable for the drive wheels. In a car, the final drive and the differential are typically joined in a single unit. In a motorcycle, the final drive is typically constituted by a chain, belt or cardan drive between the gearbox and the wheel axle.
An internal combustion engine operates optimally within a limited range of rotational speeds. The gearbox provides a variable speed ratio between the combustion engine and the drive wheels and allows for the combustion engine to operate optimally at a broader range of vehicle speeds. The gearbox also provides a variable gear ratio, and in conjunction with the final drive, it has the function of delivering a torque to the drive wheels that is suitable at the current speed of a vehicle. The gearbox is particularly important for reciprocating engines in road vehicles, due to the abovementioned minimum rotational speed, and to the fact that the road vehicles must be able to function at a wide range of speeds.
A gearbox is typically a heavy, large and expensive component in a drivetrain. There are also energy losses when converting the rotational speed from the input to the output. The strength and size of a vehicle body must be adapted to carry the gearbox, which further increases the weight of the vehicle. Thus, the weight and energy consumption of the gearbox has a negative impact on the acceleration and fuel consumption of the vehicle.
A fast acceleration is desired in many situations. Thus, it is an object of the present invention to improve the acceleration of a vehicle. It is a further object of the present invention to reduce the environmental impact of vehicle.